US3219451A

US3219451A - Sensitizing photographic media

Info

Publication number: US3219451A
Application number: US243960A
Authority: US
Inventors: Valle James E Lu; Gershon M Goldberg; John G Pack
Original assignee: Technical Operations Inc
Current assignee: Technical Operations Inc
Priority date: 1962-12-11
Filing date: 1962-12-11
Publication date: 1965-11-23
Anticipated expiration: 1982-11-23

Description

Nov. 23, 1965 J. E. w VALLE ETAL 3,219,451

SENSITIZING PHOTOGRAPHIC MEDIA Filed Dec. 11, 1962 'FIG.3.

INVENTORS.

JAMES E. LU VALLE ccasuou M. GOLDBERG JOHN s. PACK M W ATTORNEYS United States Patent O 3,219,451 SENSITIZING PEOTOGRAPHIC MEDIA James E. Lu Valle, Stony Brook, N.Y., and Gershon i Goldberg, Arlington, and John G. Pack, Reading, Mass, assignors, by mesne assignments, to Technical Operations, Incorporated, a corporation of Delaware Filed Dec. 11, 1962, Ser. No. 243,960 24 Claims. (Cl. 96-67) This application is a continuation-in-part of Serial No. 68,986, filed November 14, 1960, and Serial No. 233,199, filed October 23, 1962, the latter in turn being a continuation of Serial No. 840,973, filed September 18, 1959, now abandoned.

This invention relates in general to the field of photographic materials, and more particularly to novel sensitized silver halide photographic materials. Specifically, the present invention is directed to the sensitization of photographically responsive layers of silver halide, such as are prepared by evaporation of the silver halide from a molten pool, and the condensation of those vapors on an appropriate substrate material. The resultant stratum of condensed silver halide is formed of a large number of microcrystals which are supported on the substrate primarily by being adhered directly to each other and directly to the substrate. Such material is therefore binder-free as distinguished from conventional gelatin type photographic materials; and even if a retaining surface layer is applied over the binder-free material, the silver halide is still substantially binder-free. This material, as a photographic medium, and a process for preparing same is described in French patent, No. 1,267,623, granted June 12, 1961 to Technical Operations, Incorporated.

Other photographic media which are now known and in use are generally characterized by an emulsion or gelatin in which aggregates of photosensitive material are suspended. The use of an emulsion to hold photosensitive material on a supporting surface has many disadvantages. Among these is the fact that developing agents must penetrate the emulsion to reach the photosensitive material. Another disadvantage is the fact that there is a limit to the minimum grain size that can be achieved, due in turn to the fact that the aggregates of photosensitive material which are suspended in the emulsion cannot individually be reduced beneath a certain size Without losing or suffering diminution of their photo graphic properties. Still another is the fact that a substantial portion of the area of the photographic medium consists of gelatin, rather than photosensitive material, and this fact coupled with the minimum limit on grain size places a limitation on the fineness of detail that can be recorded. Further, the aggregates themselves are in the nature of particles of photosensitive material entrapped in globules of gelatin, so that each aggregate has the chemical characteristics of the emulsion as well as its photographic characteristics. Among the characteristics of gelatin emulsions are sensitivity to radioactive energy, such as gamma rays, and a tendency to pick up moisture, both of which cause fogging of negatives and shorten the storage life of photographic media. Further, as is well known, a gelatin, once wet, cannot be quickly dried without taking special measures which are costly and tend generally to harm the photographic image, and, as is also well known, special measures are required to bond a gelatin, which is hydrophilic in nature, to a film base, which is hydrophobic in nature. Another distinct disadvantage of known emulsion-type films is the fact that they can be used only once.

Media of the type disclosed in the aforesaid French patent generally exhibit native sensitivities, in terms of ASA speed ratings, for example in the range of 1 l0 3,219,451 Patented Nov. 23, 1965 to l 10- to white light with the response greatest in the blue region. For many photographic purposes, it is desirable to have media of higher speed, or media which exhibit a so-called panchromatic response.

It is, therefore, the principal object of this invention to impart increased sensitivity to binder-free, microcrystalline, silver halide photographic media such as those hereinbefore described.

Another object of the present invention is to provide novel processes for sensitizing such photographic media, and the products of such processes.

Yet another object of the present invention is to provide a number of novel sensitizers for such media and techniques for applying same to achieve sensitization.

Other objects of the present invention are to provide sensitization of such media by the treatment of a surface with sensitizing material applied from the vapor phase thereof; to provide sensitization of such media by treatment of a surface with sensitizing material applied from the liquid state thereof or from solution; to provide such sensitization by the vacuum deposition of sensitizing material on said surface; and to provide such sensitization by methods which can be practiced with apparatus similar to that which is used to prepare the binder-tree microcrystalline, silver-halide photographic media.

Yet other objects of the present invention are to achieve sensitization of such media through the use of single chemical elements as sensitizing materials; and to provide a number of novel sensitized photographic media.

A photographic salt, chosen from the group of silver chloride, silver bromide and silver iodide, and combinations of these, can be formed into a binder-free microcrystalline photographic medium, for example, by being evaporated in near vacuum and deposited by condensa tion in a microcrystalline form directly on a surface of a supporting medium, under controlled conditions of temperature, pressure and time. The supporting medium may be the surface of a solid material, such as glass, photographic quality paper, or photographic quality polymeric film. Alternatively, the supporting medium may be coated on the silver halide receiving surface with a bonding agent, such as a gelatin, a lacquer, or a normally tacky adhesive, in order to cause the evaporated silver halide to adhere more securely thereto.

The thickness of the resultant layer or stratum of microcrystalline silver halide photographic material which can be used can likewise vary, but preferably should be a very thin film. Some degree of photographic utility can be obtained with evaporated silver halide strata as thick as about 3.5 microns; on the other-hand, it has been found that generally there is a substantial and rapid falloil of photographic properties with thicknesses in excess of an amount around 0.3 micron. It has been found that at silver halide stratum thicknesses of around 0.3 micron one usually obtains maximum photographic properties, i.e., maximum density, speed, and gamma, one or more of which the present invention can enhance by the sensitization defined hereinafter. Depending upon the exact conditions of temperature and pressure during evaporation and condensation of the silver halide, and the particular substrate employed to collect the silver halide vapors, the exact thickness at which maximum photographic properties is obtained will vary about 0.1 0.3 micron thickness. However, the fall-oil of photographic response is usually quite rapid to either side of that thickness which provides the maximum response. Accordingly, the preferred range of thickness for the evaporated silver halide stratum, for the purposes of the present invention, is around a fraction of a micron, particularly around the 0.3 micron value, and most particularly from about 0.1 micron to about 0.5 micron.

Thus, there is provided a photographic medium consisting essentially of a continuous layer of microcrystalline photographic material, which is relatively grainless, or may be termed superfine grain, as compared with prior photographic materials prepared in suspension in an emulsion. This photographic medium has the advantages, heretofore not available, that it can be developed more easily by liquid and even gaseous developers, since there is no necessity for the developer to penetrate a gelatinous matrix to reach the photographic medium itself, that it lends itself to processes of image transfer and re-use after such transfer, and that it is practically insensitive to ionizing nuclear radiation.

Such photographic media may be made of a single one of the above-mentioned halides, or of two (or more) of them. In the latter case starting quantities of each desired halide are vacuum evaporated, in the same location or separate locations, their vapors mixed in the low pressure region if they started in separate locations, and their mixed vapors are condensed on a surface on the supporting medium. Thus, starting with appropriate quantities of silver chloride and silver bromide, a layer of silver chlorobrornide is deposited. Or, starting with appropriate quantities of silver bromide and silver iodide, a layer of silver bromoiodide is deposited. Like the single halide layer, these layers are of substantially homogenous microcrystalline form.

We have found that certain materials will enhance the photographic sensitivity of the binder-free microcrystalline silver halide layer prepared as hereinbefore described. An astonishing range of materials has been found to exist which will provide noticeable effects; many of these materials have hitherto never been suspected of being capable of providing sensitization to any type of photographic medium. These materials have been found to include, for example, generally elements of the periodic table (excluding halogens) which are normally solid, i.e., under standard conditions of temperature and pressure. The present invention is also concerned with surface sensitization achieved by processes, and the products thereof, in which diverse chemical compounds both organic and inorganic are employed as sensitizers. The incorporation of such sensitizing materials is accomplished in the present invention by several techniques. For instance, sensitizing material in some cases can be applied by evaporation and condensation from the vapor phase, as by known vacuum deposition techniques; in other instances, by precipitation procedures from solutions; and in still other instances by immersion in solutions or by coating from solution.

By the term sensitizer, without being limited to any particular theory of sensitization, it is intended to mean a material which, when applied to the microcrystalline binder-free layer of the photosensitive salt, will enhance the inherent sensitivity thereof over a predetermined spectral range, hence includes both chemical and optical sensitizers of the salt.

According to one aspect of the invention, a particulate, i.e. microcrystalline, binder-free silver halide photographic medium is sensitized by the treatment of the surface of a binder-free stratum by one or more sensitizing materials applied from the vapor phase, the deposition of the sensitizing material being accomplished substantially in vacuo and controlled to limit the amount of sensitizing material deposited.

Specifically, a binder-free silver halide photographic medium of the type described is sensitized by the deposition, e.g. from the vapor phase, onto its surface of one or more chemical elements. The deposition of the sensitizing element is controlled to limit the amount of any sensitizing element deposited to a concentration not greater than substantially atoms per square centimeter of surface of the photographic medium being sensitized to achieve media which are normally exposeable and developable into negative image bearing media.

We have discovered also that in some cases a concen' tration between the limits of 10 and 10 atoms per square centimeter of the silver halide surface of the media; provides a positive type photographic medium.

Concentration of the sensitizing deposit is controlledl in vapor deposition according to the invention by control of the pressure, temperatures of evaporation and con densation of the sensitizing element, and the time allowed"; for condensation or deposition of the sensitizing element. The resulting photosensitive medium may be untreated, or additionally chemically treated, as is hereinafter particularly set forth, to control the quality of the final sensitized product.

According to one aspect of the invention, the aforesaid medium is sensitized by treatment of the surface thereof by one or more sensitizing materials applied from a liquid phase or from solution.

In an important embodiment, the invention provides a photographic medium comprising a substrate, such as a sheet-like support of, for instance, photographicallyf inert material, having at least on one surface thereof,- with or without intervening binding strata, a binder-free microcrystalline layer of silver halide, the latter in turn being treated with a sensitizing material.

Other and further objects and features of the invention will become apparent from the following description of certain embodiments thereof and of methods and apparatus for preparing them. This description refers, for purposes of illustration, to the accompanying drawings, wherein:

FIG. 1 is a top view of a portion of a known vacuum evaporation machine which is useful in practicing the method of the invention;

FIG. 2 is a schematic side view of a portion of such a machine; and

FIG. 3 is a schematic cross-section of a sensitized medium of the invention.

FIG. 1 shows the table 11 of an existing machine for the vacuum deposition of metals and similar materials and which is employed in the invention not only to form the binder-free microcrystalline medium, but, in some cases, to apply the sensitizing material to the medium. A basic machine of the kind referred to is illustrated and described in the book Vacuum Deposition of Thin Films, by L. Holland, published by John Wiley and Sons, Inc, New York city, 1948, pages 7 and 8. A Vacuum coating; machine model LCI-14A of the Consolidated Electr cdynamics Corporation was used in achieving some of the results mentioned below. This machine has a belljar (FIG. 2) about 13 inches in diameter and 24 inches in height on the table 11 under which a low-pressure, near vacuum region is provided. The location of the bell-jar when in place on the table 11 is indicated by the dashed circle 12. The space under the bell-jar is exhausted through an opening 13 in the table 11.

Electric power terminals

15, 16, 17 and 18, 19, 20 (FIG. 1) are provided on the table 11 for supplying current for melting the silver halide source material or the sensitizing material, as the case may be, to be evapoprated in vacuum, and a pair of auxiliary terminals 21 and 22 (FIG. 1) supply operating voltage (e.g. volts, A.C.) for auxiliary devices. These terminals are all within the locus 12 of the rim of the bell jar. A first electrically conductive container, boat or filament, 24,. which may be made of molybdenum, tantalum or tung-- sten, for example, is connected by two stiff

electrical conductors

25 and 26 to a pair of the power terminals. 15 and 18, respectively. The

conductors

25 and 26 also support the open boat or filament 24 in a fixed position above the table 11. Bolts 15.1 and 18.1 (FIG. 2) fasten the free ends of these conductors to the two power ter-. minals 15 and 18, which are usually threaded for that purpose. The starting material (not shown) to be vacuum evaporated is placed in the open boat or fila ment 24.

When it is desired to vacuum evaporate two quantities of starting material in separate locations, a second boat or filament 31 can be employed, supported on two

con ductors

32 and 33, as is shown in FIG. 1. These conductors may be connected to two

separate power terminals

16 and 19, respectively, as shown in FIG. i, or if desired they may be connected to the

same power terminals

15 and 18 as the first filament 24. With two filaments connected to separate pairs of terminals as in FIG. 1, it is possible to control the current to each filament independently. Obviously, a third filament (not shown) can be added, connected to a third pair of power terminals 17 and 20, if desired.

In operation, a body or substrate 45 (FIG. 2), to be coated with the condensate from the vapor of a material (not shown) vacuum evaporated from the filament or boat 24, is supported by any suitable means (not shown) within the bell jar 14 above the filament 24 at a suitable distance therefrom. Where it is desired to form the binder-free microcrystalline silver halide medium, the starting material is at least one silver halide, chosen from the group of silver chloride, silver bromide and silver iodide. If only one of these compounds is to be coated on a surface on the body 45 a single filament 24 will sufiice. If two of these compounds are to be coated simultaneously on the body 45, for example, silver chloride and silver bromide, or silver bromide and silver iodide, a quantity of each compound may be placed on the single filament 24, or two filaments 24 and 31, as in FIG. 1, may be employed and a quantity of each compound may be placed separately on each filament. Where it is desired to sensitize the medium by evaporation, a quantity of sensitizer is placed on filament 24 and the medium is then used as body 45. In both cases the region under the bell jar 14 is evacuated to a low pressure, preferably in the range of about to about l0 millimeters of mercury, although pressures within wider limits, from 0.1 millimeter of mercury to less than 10* millimeters of mercury can be used. It is preferred to evacuate the region under the bell jar to the working pressure prior to applying heating current to the filament 24 (and filament 31, if used), so that the elevated conditions of temperature are not prolonged.

The body 45, which is the target for the vapors of the starting material, is spaced from the filament 24 (and filament 31, if used) a distance such that condensation of the vapors occurs at a condensation temperature above room temperature, preferably in the range of 30 C. to 50 C. At a pressure in the range of 10 to l0 millimeters of mercury, the temperature in the region above the filament 24 is substantially in this range at a distance about 3 /2 inches from the filament, as measured by a copper-constantan thermocouple. Under these conditions, the process is carried on for a period of time, about one minute or less to one-half hour, depending upon the temperature and pressure conditions selected, until the starting material has been deposited on the target body 45 to a desired thickness.

It is preferred that the temperature of the silver halide pool and the pressure of the system be substantially stable during the silver halide coating operation: for example, the temperature may be at about 560 C. and the pressure at about '10- mm. Hg when evaporating sil ver bromide. To attain stable values before coating of the substrate body 45 begins, a mask (not shown) may be interposed between the boat and the substrate, and after the desired temperature and pressure are obtained and stabilized, the mask would be removed and coating of the substrate would be commenced. After a desired thickness of coating is obtained, said mask may again be interposed to stop the substrate coating operation While the silver halide pool is cooled and the vacuum broken.

When forming the unsensitized medium, the substrate body 45, as shown in FIG. 2, may be a sheet of glass or alternatively, it may be a sheet of paper, plastic film, or

other conventional and suitable photographic quality substrate material. The silver halide starting material evaporated from the filament 24 in FIG. 2 condenses on a surface of the substrate sheet as a microcrystalline coating or layer. As the silver halide vapors condense on this surface, small crystal particles form and coalesce to form a tightly-packed layer wherein the crystals are sup ported on the substrate by being adhered directly to each other and to the substrate without the need of a binder. The density of a layer formed in this manner, has been measured as follows:

Using a body 45 masked by a shield having an aperture which was a square 5.7 cm. on each side, a layer of silver bromide was deposited on a surface on the body through the aperture to a mean thickness of 2.2 microns as measured by a spectrophotometer using the method of optical path ditferences between reflections of controlled light from the front and back surfaces of the layer. In this example, the thickness of the polycrystalline layer of silver bromide varied from 1.94 microns at the edge to 2.24 microns at the center. The body 45 was weighted before and after coating to obtain the weight of the layer. The volume of the layer was calculated from the dimensions of the aperture and the mean thickness, and found to be:

The weight of the silver bromide layer was found to be 0.44 gram. From these values, the density of the silver bromide layer was calculated to be 6.16 grams/ cc. The density of solid silver bromide crystals is 6.47 grams/cc. as given in the Handbook of Chemistry and Physics, 14th Edition, page 265. The ratio of the densities of this polycrystalline layer to solid crystals is therefore This indicates that the layer 46 is very tightly packed and has a density closely comparable to that of the solid crystal of the starting material.

The polycrystalline layer of silver halide can be deposited also on a bonding type of substrate, as suggested above. The supporting body, for example, can be a film made of a cellulose derivative or other polymers. This film has on one surface a subbing stratum of soft material, such as a layer of shellac or a water-permeable colloid, for example, gelatin. The evaporated layer of silver halide is deposited on the subbing stratum. Due to the softness of the subbing stratum, the first crystal particles of the silver halide which are deposited on it penetrate somewhat, and the coalescense of subsequent particles of the silver halide on the initial particles serves to bind the silver halide crystal layer to the supporting body somewhat more securely than had the subbing stratum not been employed. Obviously, a glass body can be used in place of the synthetic resin body if desired.

If it is desired to fix an image on a sample of the original photographic medium, the use of a layer 46 sufiiciently thin to result in development of the image through the entire thickness of the layer will prevent re moval of the image when the remaining silver halide is dissolved in the fixing bath. Otherwise, upon dissolution of the underlying silver halide, the silver image floats 01?. Alternatively, a liquid pervious retaining sheet can be first applied to retain the developed image, and then dissolution of silver halide in the fixer will not cause loss of the developed silver particles. Rather than em ploy such expedients as this, it is preferred to use silver halide strata which are sufficiently thin to result in development of light struck areas down to the supporting substrate, whether or not surface protective layers or sheets are employed. Since the crystal structure resulting from the present process of evaporating silver halide provides a continuity of contact between grains both laterally across the face of the photographic material as well as downwardly through the silver bromide layer to 95.3 percent the substrate support material, the development process :spreads laterally from a light struck to adjacent grains :as well as downwardly through the thickness of the layer. Therefore, if the thickness of the silver halide layer is too great, development down to the substrate can result in an intolerable loss of acutance and image sharpness. It has been found that a silver halide layer of about 0.3 micron in thickness can be developed down to the substrate without appreciable loss of image sharpness and without fogging.

In view of the fact that maximum speed, density, and gamma, are all obtained without a 0.3 micron thick layer of silver halide, and since the ability to develope down to the substrate without noticeable loss of image sharpness or fogging is likewise obtained at this thickness of around 0.3 micron, it is apparent that this thickness provides the approximate optimum for the sensitized photographic material of the present invention. These factors however are not intended to exclude entirely slightly thicker layers of silver halide, of say up to about 3.5 microns, from the scope of this invention, since such layers can be used where the maximum properties are not essential or desired and other considerations outweigh the loss of photographic properties suffered, such as are suggested in the aforesaid French patent.

As materials which can be evaporated onto a surface to provide sensitization of the microcrystalline binder-free silver halide are normally (i.e. under standard conditions of temperature and pressure) solid elements other than halogens, selected from the group of elements of the periodic table classified in Groups I through VI and VIII. Specific examples of chemical elements which we have vapor deposited on the outer surface of a microcrystalline, binder-free silver halide photographic medium to of coating level or concentration is set forth in two columns entitled respectively Normal and Solarized and a column also has been included entitled Fogged. Where all three, or two of three, of the above can be achieved, fogging is obtained with the thickest (or thicker of the two) coatings of the elemnt involved. Inasmuch as fogging is undesirable, detracting from the photographic qualities of images, conditions wherein fog occurs should be avoided generally. Where normal and solarized images are obtained with a given element, the thicker layer, i.e. the heaviest concentration, yields the solarized image. In general, where a normal image is obtained, the layer of sensitizer material is not substantially greater than 10 atoms per square centimeter of adjacent surface of the photographic silver halide. Layers in heavier concentration yield either solarized images or fogging.

The last three columns set forth the approximate pressure in millimeters of mercury, time used for achieving appropriate deposition of the sensitizer vapor, and either the voltage or current through a filament, at which voltage or current, satisfactory vapor deposition of the element is obtained. The filament used in most cases in Table I is tungsten and has approximate dimensions of 0.75 x 2.215 x 0.002 inches. In some cases, a tantalum filament or other filament material is preferably employed to avoid having a filament with which the starting material reacts chemically. For instance, for vapor depositing antimony and bismuth a tantalum filament is preferred. The teachings of Holland at pages 110-114 in his aforesaid book can be followed in many cases, particularly in the use of a boat form of filament.

To obtain the results set forth in Table I starting quantities of 10 milligrams or less of each element are employed) TABLE I Results obtained as function of coating level Evaporation conditions for normal image Normal image solarized image Pressure Volts or Fogged amps Time (sec) 73 amps. 3 amps. amps. 90 amps. 2 amps. 25 amps. 43 amps. volts. 55 volts. 70 amps. volts. 135 volts. 180 amps. 75 volts. 15 volts. volts. 18 amps. 2.2 volts. 40 volts. 40 volts. 25 amps. 56 volts. amps. amps.

N 4 4 4NNNNNNNNNMNNNNNNNNNNNNMNNNNNNN 44 amps.

increase the photographic sensitivity thereof and with which, in each case, there can be obtained upon standard exposure and development a normal (i.e. a negative) image, a solarized (i.e. direct positive) image or both, are set forth in tabular form in Table I following. In this The media sensitized to provide normal images, upon exposures of relatively short duration, for example second, and subsequent development will of course yield negative images. However, some of these media, if exposed instead for relatively long periods, for example 30 table, the type of image ultimately achieved as a function 75 seconds, will exhibit a tendency to solarize. This solarization tendency can be inhibited by treatment, as by immersion, in a solution of milligrams of ammonium chloroiridite per liter of water and subsequent drying before exposure.

Deposition of elemental materials can also be achieved from solution. This of particular value in such cases as the use of sulphur and selenium because these latter are diflicult to control in a vapor deposition process owing to their relatively high vapor pressures at relatively low temperatures. A layer of sulphur, for instance can be deposited from solution using a colloidal suspension of sulphur in dioxane, a quick evaporation vehicle identified in the Merck Index 7th edition, page 387, published 1960 by Merck & Co., Inc. of New Jersey. Selenium and sulphur can be deposited, each from a solution in dimethyl sulfoxide (Merck Index) ibid page 373. In each latter case a saturated solution is employed at room temperature, and the precipitant is washed with water with which dimethyl sulfoxide is miscible and in which the precipitant is relatively insoluble.

Such reactions as may take place at the silver halide surface in contact with elements of widely varying properties (e.g., sodium, gold, selenium) were not expected to be the same, and as Table I indicates, the conditions for achieving a sensitized medium which will yield a normal image do indeed vary considerably from one element to the next. In certain cases, such as that of sodium, which is difiicult to work with because it tends to react with moisture and sputters when heated, greater precision of control of conditions is necessary to achieve desired images. Our investigation of the thirty-five elements mentioned above indicates, however, that any element, with the exception of Group VII A, the inert gases, the halogens, nitrogen, hydrogen and possibly oxygen, which can be handled in a vapor deposition apparatus can be deposited on the surface of a binder-free silver bromide photographic medium and can be expected to enhance the sensitivity thereof.

The foregoing methods of the invention can be used with many forms of binder-free silver halide photographic medium. One embodiment is shown in FIG. 3 wherein is shown a binder-free, microcrystalline silver-halide layer 51.20 held on a base 51.22 by, for example, subbing layer 51.21. On the top or outer surface of this layer (as seen in the figure) there is a layer 52 of sensitizing material. This layer 52 is illustrated exaggerated in size. The layer is, however, thinner than the drawing indicates, being made of approximately 10 atoms per square centimeter of the surface of silver halide on which it rests, as is mentioned above. It would be impractical to attempt to illustrate the sensitizing layer to true scale; it should be regarded as an approximately monoatomic layer. The sensitizer 52 obviously has its principal or primary effect on the photolytic sensitivity of the surface microcrystals in layer 51.20 with which the sensitizer material is in contact.

We have made sensitometric measurements, in a sensitometer adapted for exposing light of 5500 K. color temperature through a brightness range of 100 to 1, in steps of transmission density changing in increments of 0.20, onto binder-free microcrystalline sensitized media according to FIG. 3. This sensitometer used a ZOO-watt tungsten lamp with a Corning No. 5900 correcting filter as the source of 5500 K. light, a sector wheel driven at controlled speed as a timing device, and a step wedge (obtained from Eastman Kodak Company, Rochester, New York) having steps of transmission density varying from 0.05 to 3.05 in increments of 0.20. The speed thus determined of such media sensitized according to the invention is of the order of ASA 0.10, a tenfold increase. These speed values were measured using the surface developer described hereinafter. Higher speed values can be obtained with other developers.

We have made photographs of printed material consisting of black characters on a white background using binder-free photographic media sensitized according to the invention. Examples of the results obtained are as follows:

(1) Lead-sensitized medium.Exposed for V5 second at f/4; developed in 10 seconds; yielded a normal (negative) image.

(2) Copper-sensitized medium.Exposed for 3& second at f/4; developed in 30 seconds; yielded a normal (negative) image.

(3) Gallium-sensitized medium.EXp0sed for /5 second at f/4; developed in 30 seconds; yielded a normal (negative) image.

(4) Zinc-sensitized medium.Exposed for /5 second at f/4; developed in 15 seconds; yielded a normal (negative) image.

(5) Selenium-sensitized medium.30 seconds in ammonium chloroiridite solution following vapor deposition of selenium; exposed for second at ;f/4; developed in 10 seconds; yielded a solarized (direct positive) image which was the complete reverse of a normal (negative) image.

These photographs were all contact-printed through a transparency, using a mercury lamp emitting light through a lens system and an adjustable lens stop. With the stop set at f=3.5, the light intensity one foot from the lamp was 35 lumens per square foot. The transparency was set against the medium, at a distance of one foot from the lamp. The f settings stated in the foregoing examples were the settings of the lens stop of the lens system.

We have obtained comparable results with silver bromide photographic media sensitized, by sulphur or selenium, for example, deposited from solution or suspension, as described above.

Among the chemical compounds found which may be vapor deposited onto microcrystalline binder-free silver halide medium to sensitize the latter are organic compounds such as dyes selected from those which are evaporatable Without substantial decomposition below approximately 300 C. Typical of the cyanine dyes which can be sublimed at reduced pressure are those disclosed in Experiments on the Electronic Mechanism of the Photoconductivity of Sensitizing Dyes, H. Meier, Phot. Sc. & Eng, vol. 6, #4, p. 235 An example of optical sensitization of a microcrystalline binder-free silver halide medium in this novel manner is as follows:

Example 1 A quantity of 1,1 diethyl-2,2' carbocyanine chloride (pinacyanol) is sublimed at reduced ambient pressure of about l 10 mm. of Hg at a temperature of approximately 200 C. onto a microcrystalline, binder-free silver halide layer lying on a subbed polyethylene terephthalate sheet to produce a visible dye layer of substantially uniform distribution at a concentration of approximately a microgram per 70 square mm. of silver halide surface. Exposure of a portion of the medium for 0.1 sec. to a lamp corrected to 5500 K. through a Wratten 25 filter and development in an internal developer produces no indication of red sensitivity. However, after wetting the dye surface of the unexposed portion of the medium with pure water and drying, upon the same exposure and development, the medium shows a red speed of the order of ASA 4X10- and a white light speed of the order of IX 10- This procedure is particularly effective to sensitize microcrystalline binder-free silver halide media with appropriately vaporizable dyes that are poorly soluble or relatively insoluble in aqueous solution. The application of water in the last step is believed to provide the necessary aggregation of dye molecules adsorbed on the silver halide.

to the use of these specific compounds.

Obviously, by this method, concentrations of some dyes can be applied to such media, which concentration could not be possibly achieved through application from aqueous or alcohol solutions.

Condensation products of alkylene oxides can be employed to increase sensitivity of microcrystalline binderfree silver halide by simply applying the material to the surface of the silver halide layer. Alkylene oxide polymers, generally referred to herein as polyglycols, may be formed from monomers which contain 2 to 4 carbon atoms, e.g. ethylene, propylene and butylene oxides, as is well known in the art. Likewise condensation products of alkylene oxide with other oragnic compounds may also be used as sensitizers. Polyglycols of these types have been used, either alone or in combination with other sensitizers, as sensitizers with gelatin-type silver'halide emul- SlOIlS.

The'use of alkylene oxide derivatives to sensitize microcrystalline binder-free silver halide media according to the present invention are illustrated in the following specific example, although the invention is no way limited This example takes the form of a table in which all of the compounds were applied in 0.5% aqueous solutions and the medium was immersed therein for V2 hour at room temperature. In each case, development was made thereafter with an internal developer following a standard exposure. Unsensitized material used for control in each case showed a sensitivity on a sensitometric step wedge of 10 steps.

Example 2 Trade name Chemical name pH Results Amidox L Ethoxylated amides 8.20 13 steps. Amidox C5.-- .-.do 8.40 D0. Macon 1O Nonyl phenol ethylene 6. 45 14 steps.

oxide condensates. Stepanol 153 Ammonium alkyl phenoxy 5.80 13 steps.

polyoxyethylene sulfate. Stepanol TBK Alkoxy polyoxyethylene 4. 70 D0.

ethanol.

All materials shown in the foregoing table were obtained from Stepan Chemical Company, Chicago, Illinois, and

a the chemical name thereof given is believed to be the most Example 3 A microcrystalline binder-free silver halide medium of the type described was immersed for two minutes in an 0.1 M triethanolamine solution at room temperature, subsequently washed in distilled water and shaken dry. The sensitized medium, upon exposure and development in an internal developer, showed an ASA speed of about 0.1. Similarly, individual solutions of triethanolamine alkylaryl sulfonate and triethanolamine lauryl sulfate (the aforesaid being available under the trade names respectively of Ninex and Stepanol WAT and obtained from the Stepan Chemical Company) also provided comparable sensitization. A microcrystalline binder-free silver halide medium of the type described was also immersed in an aqueous solution of about-0.1 M of ethylene diamine tetra acetic acid in the sodium salt form. This was found to increase the film speed by a factor of about 2 also. Variations between about 3 to 11 with respect to the pH of the solution deliberately introduced in the use described above of triethanolamine alkylaryl sulfonate as a sensitizer, provided no essential change in the sensitization achieved. While /2 hour appeared to be the optimum time for treatment of the medium with the polyamines, treatment of the silver halide surface for as little as 1 minute showed a significant sensitization effect.

Among the organic compounds found to act as sensitizers of the media employed in the present invention are certain organic sulfoxides which can be represented by the following general formula:

wherein both R and R are various aliphatic or aromatic groups substituted and unsubstituted (e.g. alkyl groups such as methyl, ethyl, propyl, butyl, etc.; aryl groups such as tolyl, phenyl, etc.; and aralkyl groups such as benzyl, fi-phenethyl, etc.; alkylene groups such as ethenyl propenyl, etc.). The radicals represented by R and R can also be substituted by functional groups containing, for instance, sulfur, nitrogen or oxygen such as mercapto, amino, methylamino, hydroxyl, methoxyl, etc., as well as the usual halogens. Use of the above organic sulfoxides is illustrated in the following example:

Example 4 Individual solutions of dimethyl sulfoxide, diethyl sulfoxide, dibenzyl sulfoxide, diphenyl sulfoxide and di-ptolyl sulfoxide were prepared, each by dissolving 20 grams of pure material in a respective liter of ethanol. Another solution of dimethyl sulfoxide was prepared by dissolving 20 grams thereof in a liter of water, the other sulfoxides being too insoluble to prepare such aqueous solutions. Individual samples of microcrystalline binderfree silver halide media of the type described were immersed each in one of the above solutions for 5 minutes and allowed to dry. Upon exposure of each for 0.1 second, followed by development in surface developer for 30 seconds, in each instance effective sensitization by a factor of at least 2 over unsensitized control media Was achieved. Similar procedures carried out with diethyl sulfite (which can be described as diethoxy sulfoxide) yielded no increase in sensitivity, indicating that the presence of an oxygen linkage between the sulfur atom and the radicals R and R was inimical to the phenomenon. Similarly, upon the use of further oxidation products, i.e. the sulfones, sensitization of this magnitude was not observed.

The microcrystalline binder-free silver halide medium used in the invention can also be chemically sensitized with dyes as shown in the following:

Example 5 A microcrystalline binder-free medium of the type described was first immersed in a 20 mg./l. aqueous solution of Na Au (S O for 30 seconds, dried and then immersed in a solution of 1,l-diethyl-2,2-cyanine bromide for 5 minutes. The latter solution was prepared by dissolving 0.1 mg. of the dye in 1 liter of water. The medium was then shaken dry and exposed in a sensitometer. Upon development in a surface developer, the medium was found to have its sensitivity to white light enhanced by about 1 /2 orders of magnitude over the control medium similarly sensitized with the gold salt alone.

It is of interest to note that this dye is known as an optical sensitizer for chloro-bromide emulsions, but surprisingly acted in this instance as a chemical sensitizer rather than an optical sensitizer. Exposure of the sensitized medium to light in the absorption band of the dye established that no optical sensitization as such was achieved.

The type of media used in the invention may be also sensitized with certain organic and well-known reducing agents known as the complexed borane hydrides, as will be seen in the following example:

Example 6 A microcrystalline binder-free medium of the type described was immersed in a solution of dimethylamineborane in water for 30 to 60 seconds, washed with water and allowed to dry in air. Upon exposure and surface development, it was found that the medium was sensitized by approximately an order of magnitude in comparison with a controlled unsensitized medium similarly exposed and developed. Similar results were also achieved using comparable solutions of methylamineborane, pyridine borane and sodium borohydride.

It has also been found that a number of inorganic compounds may be applied in solution to the surface of a microcrystalline binder-free silver halide medium to chemically sensitize the latter. In some instances the sensitizing material is quite novel.

For instance, the treatment of substantially binder-free microcrystalline silver halide media with copper ions from solution has resulted in markedly increasing the photographic sensitivity of the silver halide. That copper ions either in cuprous or cupric form, can act as sensitizers was totally unexpected. Indeed, copper salts added to emulsion before the growth of silver halide grains has been shown to severely reduce sensitivity according to the article, Effect of Metal Ion on the Photographic Emulsion, by Shono, Fukuda and Fukawa in the Scientific Publications of the Fuji Photo Film Co., Ltd, 1, 69, 1953. To similar effect is the article by Charriou, Compt. Rend., 19489 (1935).

The unexpected enhancement of photographic sensitivity of evaporated film by copper ions is illustrated in the following examples:

Example 7 A aqueous solution of cupric chloride was prepared. Iust before use, 1 ml. of this solution was diluted to 50 ml. with water. A microcrystalline medium of the type described was immersed in the dilute cupric chloride solution for two minutes and shaken dry. The treated film was exposed in a step-wedge sensitometer to a light source corrected to approximately 5500 K. and developed in an internal developer solution for sec. at 25 C. Sensitometric results indicated that an increase in sensitivity by a factor of about 1 /2 over unsensitized control media was achieved.

Example 8 Example 9 An unsensitized microcrystalline, binder-free medium of the type described was immersed for one minute in the 25% solution of cupric chloride at room temperature. The adsorbed cupric ion was converted to cuprous ion by immersing the medium in a mixed solution of 0.1 M sodium bisulfite and 0.1 M sodium bromide for 15 seconds. Upon exposure and development in the same manner as set forth in Example 8, sensitometric results from the developed medium indicated that the photographic sensitivity thereof had been increased by a factor of approximately 2, somewhat more than had been achieved with cupric ion alone. As in Example 8, the sensitivity could be further enhanced if following conversion of the cupric ion to cuprous ion, the medium was then immersed for 15 seconds in an 0.5% EDTA solution.

Other inorganic salts in aqueous solution can be employed as sensitizing agents for the media heretofore described as illustrated in the following example:

Example 10 Binder-free silver halide media of the type described were immersed in 0.2 M solutions of respectively ammonium bromide and ammonium acetate, and then dried. In both cases, following exposure and development in an internal developer, sensitization by at least a factor of 2 was achieved. Optimum results were obtained by immersion in the respective solutions at 40 C. for 30 minutes, although reasonable results could be obtained after 5 minutes.

It has also been found that the photographic sensitivity of the silver halide in microcrystalline media of the type heretofore described can be enhanced with hydroxyl ions provided from inorganic bases. Examples of such sensitization are as follows:

Example 11 A microcrystalline binder-free silver bromide layer evaporated onto a polyethylene terephthalate sheet was immersed at room temperature for 30 seconds in an 0.04 N solution of sodium hydroxide and then dried. Following exposure and development for 30 seconds in a surface developer, this treatment was found to have increased the sensitivity of the medium by a factor of 4 over the photographic sensitivity of an unsensitized control medium.

Example 12 An unsensitized medium similar to that heretofore described in Example 11 was immersed for 5 minutes in a 4% ammonium hydroxide solution and then dried, exposed and developed for 30 seconds in a surface developer. The sensitization achieved was approximately the same as that resulting from treatment with sodium hydroxide.

In all the preceding examples, and in the preparation of the unsensitized evaporated film used therein, the highest purity materials obtainable were employed to insure that the effects noted were not due to unknown impurities.

The surface developer which is used in the examples hereinbefore described is prepared and used as follows. Three stock solutions are prepared, preferably using triplydistilled water. These solutions are:

in 250 cc. of water;

Sodium carbonate (anhydr) 78.00 If monohydrate, use 91.26 Potassium bromide 2.0

in 1 liter of water;

Gelatine plus water to make 250 cc.

Solution (a) decomposes with time, solution (b) keeps indefinitely, and solution (c) should be kept refrigerated to inhibit decomposition.

These solutions are used in equal proportions to make the developer. They are mixed by adding ml. quantities of, first, solution (b) to solution (a), and then 20 ml. of solution (c) to the mixtures of solutions (a) and (b).

The internal developer used in some of the examples is formed in the same manner, but to the mixture of (a), (b) and (c), 3 ml. of a 1% sodium thiosulfate solution is then added.

From the foregoing description of the inventiton and the numerous examples described, it will be appreciated that we have discovered that the evaporated binder-free silver halide medium hereinabove described can be effectively sensitized for photographic purposes. Since the silver halide medium of the present invention is dry formed under high temperature and vacuum evaporation, to form a very dense microcrystalline stratum, as distinguished from the conventional wet formed gelatine emulsion silver halide media, the two media are not analogous. Indeed, the examples of this specification show: that some materials that act as sensitizers for one medium, act as desensitizers for the other; that some materials that act as dye sensitizers for one medium, act as chemical sensitizers for the other; and that some materials that do not act or are unknown as sensitizers for the gelatine types medium shown herein to be sensitizers for the evaporated binder-free medium. From the foregoing it will also be apparent that our invention is particularly concerned with the sensitization of very thin layers of evaporated binder-free silver halide material, i.e., layers having a thickness of from about 0.1 to about 0.5 micron in thickness.

Since certain changes may be made in the above product and process without departing from the scope of the invention herein involved it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted in an illustrative and not in a limiting sense.

What is claimed is:

1. An image recording medium comprising a substrate element having a surface providing a recording area, a photographic layer of vapor deposited photosensitive silver halide microcrystals in substantially continuous phase supported upon said element and substantially covering the extent of said area, said layer being adhered directly to said substrate and said microcrystals being cohered directly to each other, said layer having a density less than that of said halide in solid crystalline form, said layer being a fraction of a micron in thickness, and a surface portion of said layer over said area having been treated with a sensitizing material to provide an increased photographic sensitivity for said surface portion.

2. An image recording medium as set forth in claim 1, the extent of said area, said layer being adhered directly to about 0.5 micron.

3. An image recording medium as set forth in claim 1, wherein said silver halide is silver bromide.

4. An image recording medium as set forth in claim 1, wherein said silver halide comprises a plurality of halides.

5. An image recording medium as set forth in claim 1, 'wherein said density is about 95% of that of said halide :in solid crystalline form.

6. An image recording medium as set forth in claim 1, :and further having a protective layer of material overlying said stratum and cohered to the surface thereof and sandwiching it between said layer and said substrate.

7. An image recording medium as set forth in claim 1, wherein said thickness is about 0.3 micron.

8. An image recording medium as set forth in claim 1, wherein said surface portion of said layer is that surface portion remote from said substrate element.

9. A silver halide photographic element comprising a substrate sheet having a surface providing a recording area, and a photoresponsive layer having a stratum of substantially binder-free, vapor deposited silver halide microcrystals supported on said surface of said sheet and substantially covering said area of said sheet, said stratum having a thickness of a fraction of a micron and a density of less than that of said halide in solid crystalline form, said layer further including a photosensitizer for said halide applied and distributed substantially uniformly over a surface of said stratum over said area.

14). An element as set forth in claim 9, wherein said thickness is from about 0.1 to about 0.5 micron.

11. An element as set forth in claim 9, wherein said photosensitizer is a material selected from the group consisting of titanium, silver, aluminum, arsenic, gold, barium, beryllium, bismuth, cadmium, cobalt, chromium, copper, iron, gallium, germanium, indium, manganese, magnesium, sodium, nickel, neodymium, lead, palladium, praseodymium, praseodymium, platinum, antimony, selenium, silicon, tin tellurium thallium vanadium zinc samarium and sulfur.

12. An element as set forth in claim 11 wherein said photosensitizer also includes a chloroiridite salt.

13. An element as set forth in claim 11, wherein said thickness is from about 0.1 to about 0.5 micron.

14. An element as set forth in claim 11, and further having a protective layer of material overlying said photoresponsive layer and cohered to the surface thereof and sandwiching it between said protective layer and said substrate sheet.

15. An element as set forth in claim 11, wherein said surface of said stratum is that surface remote from said substrate sheet.

16. A method of forming a silver halide photographic element, comprising evaporating silver halide under a high vacuum with said silver halide at a temperature in excess of its melting point, condensing the silver halide vapors over a surface area of a base member to form a layer of light responsive silver halide upon said base as a support therefor, said evaporation being conducted from a pool of molten silver halide, said evaporation and condensation being effected under substantially stable conditions of pressure and temperature to afford substantially uniform characteristics to the silver halide deposit, and wherein said silver halide is deposited to a thickness sufficient to cover substantially said entire area of said base member but no greater than a fraction of a micron, and applying a silver halide photosensitizer to the surface of said silver halide layer.

17. A method as set forth in claim 16, wherein said thickness is between about 0.1 and about 0.5 micron.

18. A method as set forth in claim 16, wherein said photosensitizer is applied by vapor deposition thereof onto said silver halide surface.

19. A method as set forth in claim 18, said vapor deposition is effected under high vacuum.

20. A method as set forth in claim 16, wherein said photosensitizer is applied by immersing said layer in a liquid medium containing said photosensitizer.

21. A silver halide photographic element comprising a substrate element, a photoresponsive layer having a stratum of substantially binder-free, vapor deposited silver halide microcrystals supported by said element and substantially covering an image recording surface area thereof, said stratum having a density less than that of said halide in solid crystalline form, a surface portion of said stratum over said area having been treated with a sensitizing material to provide a photolytic sensitivity greater than that of the adjacent portion of said stratum and a protective layer of material overlying said photoresponsive layer and cohered to the surface thereof and sandwiching it between said protective layer and said substrate element.

22. A photographic element as set forth in claim 21,

1 7 wherein said surface portion of said stratum is that surface portion remote from said substrate.

23. A photographic element as set forth in claim 21, wherein said surface portion of said stratum has a photosensitizer for said halide applied and distributed substantially uniformly thereover.

24. A photographic element as set forth in claim 23, wherein said surface portion of said stratum is that surface portion remote from said substrate.

6/1961 France. 9/1958 Great Britain.

18 OTHER REFERENCES Evans et al.: Journal of Photographic Science, vol. 3, pages 73-87 (1955).

Nail et 211.: Physical Review, vol. 98, page 1557 (1955).

Nelson: Journal of Optical Soc. of America, vol. 46, pp. 1016-9 (1956).

Moser et 211.: Physical Review, vol. 102, pp. 1519-23 (1956).

Yamada et al.: Chemical Abstracts, vol. 50, pages 11147-8 (1956).

NORMAN G. TORCHIN, Primary Examiner.